Many metal-containing devices and structures must function in corrosive atmospheres which cause them to deteriorate over time. Corrosion may take the form of metal oxides resulting from reaction with oxygen in the air, or by compounds formed with the effluent of industrial processes, such as hydrogen sulfide.
In the electronics industry, for example, approximately one-third of all warranty repair work is attributable to corrosion. Accordingly, the ability to accurately monitor corrosion and take appropriate measures to deter its spread are of utmost importance to the industry.
The standard method of monitoring corrosion has historically been accomplished using a reactivity monitoring procedure such as the so-called “coupon” method. In this method, strips of copper are placed in the environment where corrosion is to be monitored. The coupons carry an initial copper oxide corrosion thickness of about 100 Angstroms (A). After a period of time in the environment, usually around thirty to ninety days, the coupon is collected and the change in thickness of corrosive buildup on the strips, or coupons, is measured using a complex coulometric reduction procedure, well known to those skilled in the art.
Using an accepted standard such as Standard No. ISA 71.04-2013 set by the International Society of Automation (“ISA”) of Research Triangle Park, N.C. (attached hereto and incorporated in its entirety by this reference), this change in thickness is then projected over a chosen period of time. This standard has been endorsed by several trade groups/organizations, including the International Electronics Manufacturing Initiative (“iNEMI”) (see attached, incorporated in its entirety by this reference). Other organizations, such as Battelle of Columbus, Ohio, have also developed such standards which, like the ISA standard, are based on reactivity monitoring techniques. Given a corrosive buildup after any number of days, the standard may be applied to project the weekly, monthly, or annual buildup of corrosion in the environment. Such information is vital to the electronics industry in determining the reliability and projected lifetime of equipment. It may affect the scope or duration of warranty coverage, particularly in limiting such coverage when the equipment will be used in corrosive environments. The reactivity monitoring method of corrosion monitoring using coupons is discussed in further detail in “Environmental Conditions and Process Measurement and Control Systems: Airborne Contaminants,” a 1985 ISA publication; and Krumbein, Newell, and Pascucci, “Monitoring Environmental Tests by Coulometric Reduction of Metallic Control Samples,” Journal of Testing and Evaluation, Vol. 17, No. 6, November 1989, pp. 357-67, both of which are incorporated herein in their entirety by this reference.
One major disadvantage of the coupon method of corrosion monitoring is the time frame needed to place the coupon and then analyze the coupon. The coupon method is a passive corrosion monitoring system that cannot provide instantaneous feedback when a certain corrosion threshold is reached.
Real-time corrosion monitoring has been achieved by using quartz crystal microbalance (“QCM”) based sensor systems that measure the change in frequency of a quartz crystal resonator caused by the loss or addition of a mass due to corrosion of the sensor. While QCM-based corrosion monitoring systems can provide real-time information regarding corrosion in an environment, such systems are complicated and expensive.